Increase in crash-worthiness is an ongoing challenge for the manufacturer of aircraft such as helicopters. The aircraft must be strong enough to maintain integrity of structure defining the crew and passenger compartments while being able to deform so that injurious loads are not transmitted to occupants. If there is no crush zone under a helicopter floor, crashes are characterized by high peak loads that can heave up the floor resulting in loss of structural integrity of the fuselage and the structure for seating and for support of large masses such as the propulsion system comprising the transmission and rotor. Ideally, a fuselage should absorb crash energy to control deformation of a crush zone without exceeding the structural capability of the floor and the structure supporting the propulsion system. The aim is to have the components of the helicopter stay in place and the passenger area retain its shape.
Heretofore metals which absorb energy through plastic deformation have been the prime material utilized in attempts to provide crash-worthy structures.
Currently, composite materials are used for the construction of airframes. Composite materials as used herein shall be taken to mean fiber reinforced plastic materials. Composite materials are being used because of reduced cost, reduced weight and improved corrosion resistence. However, such materials are not characterized by having plasticity and therefore must absorb energy by other means.